Seasonal Pattern of PM2.5

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Seasonal Pattern of PM2.5

• Background and Rationale
• Some Causes of Seasonal PM Variation
• PM10-PM2.5 Relationship over the Northeast and
  Southern California
• Seasonal Charts of PM2.5
• Resource Links

Contact Bret Schichtel, Bret_at_mecf.wuslt.edu
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Background and Rationale

• The seasonal cycle results from changes in PM
  background levels, emissions, atmospheric
  dilution, as well as chemical/removal processes.
• Examining the seasonal cycles of PM2.5 mass and
  its elemental constituents can provide insights
  into these causal factors.
• The season with the highest concentrations is a
  good candidate for PM2.5 control actions.

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Some Causes of Seasonal PM Variation

• In urban areas, the winter mixing heights are
  low trapping emission due to the poor
  ventilation. In the summer, intense vertical
  mixing raises the mixing heights which tends to
  dilute the concentrations.

• PM primary and precursor emissions are
  seasonally dependent due to seasonal changes in
  energy consumption for heading and cooling,
  fires, etc.
• Many of the gas to particle transformation rates
  are photochemically driven and peak in the summer

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PM10-PM2.5 Relationship over the Northeast and
Southern California
In Southern California, the PM2.5 peaks in the
winter with 2.5 times more mass than during the
spring and summer. The PM10 peaks in the fall.
In the Northeast PM2.5 and PM10 are summer peaked
with approximately 30 more mass in the summer
than the winter.
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Seasonal Charts of PM2.5
Urban Southwestern sites are winter peaked with
50 more PM2.5 during December than July. The
rural sites are spring-summer peaked with 50
more PM2.5 during June than Jan.

• At Washington DC and Philadelphia, the PM2.5
  increases 60 from winter to summer.
• In the Rural Appalachians the summer PM2.5 is a
  factor of three higher than during the winter.

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Resource Links

• Workbook Table of Contents
• Comment and Feedback Page
• Applications / Reports
• Data sets used in the Applications
• Methods and tools used in the Applications